That rotten egg smell hanging over parts of South San Diego today was not a mystery plumbing problem. County officials issued an air quality advisory after monitoring stations detected elevated levels of hydrogen sulfide across South San Diego County.
The foul odor associated with hydrogen sulfide (H2S) is more than just annoying. At higher concentrations, it can trigger headaches, nausea, and respiratory irritation. Health officials warned that children, older adults, and people with breathing or heart conditions should be especially careful whenever the smell is noticeable.
The San Diego County Air Pollution Control District posted the alert on X, flagging “South San Diego County Communities” as affected and directing residents to more information and local guidance, according to the San Diego County Air Pollution Control District. The advisory pointed people to the agency’s community hydrogen sulfide guidance and an information page with tips on keeping indoor air as clean as possible during odor events.
— San Diego County Air Pollution Control District (@sdapcd) February 5, 2026
What the readings mean
A peer‑reviewed study led by UC San Diego documented short hydrogen sulfide spikes as high as 4,500 parts per billion and one‑hour averages near 2,100 parts per billion at a hotspot in the Tijuana River Valley, linking river flows to airborne pollution, according to UC San Diego. For context, California’s one‑hour hydrogen sulfide standard is 30 parts per billion, and state public health reviews put long‑term guidance in the single‑digit parts‑per‑billion range, according to PubMed Central, underscoring how far those measured peaks shot past public health thresholds.
How to protect your home and family
County air officials advise staying indoors when the rotten egg odor is noticeable, cutting back on vigorous outdoor activity, and seeking medical care if symptoms such as headaches, nausea, or breathing problems become persistent or severe…